Conducting seal for high-pressure lamps



1952 E. H. NELSON ETAL 2,583,388

CONDUCTING SEAL FOR HIGH-PRESSURE LAMPS Filed se t. 14, 1948 ITWVGTTECDTSI Evan fievb eri NeLson, Evnes=-l7 Benjamin Power,

Their A hlrovneg.

Patented Jan. 22, 1952 f Evan Herbert Nelson; HarrowWeaIld, and "Ernest Benjamin PoWenI'Kenton, England, assignors 10-Genersfl Electric Company,*a corporation of New .York

"mlicaitlcnsep'teifiber 14,19is;1serin no. 49,144

1- Qlaim.

' g I 51 This inventionrelates'ito oonductorz seail" he dies "IrKGrreat Bi'itain .May 1, 1947 and sealed to a button of glasswwnicnshuttoniis 'itself sealed around the -rod to form a vacuumtight seal. g

Thetemn 'butto'nf does not@irhply any iparticular shape for the body ofzglass Icons'tituting th'e button, but in generali-iitxi'stfound desirabiez' that the button should eonsist'oi ashor't .sl'eeve sealed arouridthe rod rand-a flange extending tram-the sleeve for an appreciabledistance approximately 1 sit right angles to theaxisipf' 'the rod.

f I'Joriductor-seaitbodies: of. tneitype specified: are often used tor sealing -a' conductor through -the vitreous envelope of -an electiici di-scharge device.

the tube of vitreous material'containing the'ponductor being sealed "to 'the'si'des of Whblefifi the envelope through which the conductor :1 passes.

"In some cases the envelope is of har-d vitreous material to withstand heat developed during operation of the device, and"it tis then desirable *that the tube or (the conduotor seal" body should .be' of similar hard vitreous rmaterlal and" should be sealed to themetalrod'"conductor through a button (if intermediatenglass.

*By hard vitreous mater iai is rnean-tfafor 'the purpose of this speoincatlonpa vitreous material *'whose the'rm al expansion coefneient' isifsoimuch "less than that-#01" the Pmetal of the red that ii: 1 cannot be sealedd'irectlytothe rod nfitbout considerable risk of cracking of the-seal onhea fiing. The vitreous' material and'rod'metal particularly contemplated for "use vii th this invention fare quartz and tungsten; respectively.

' Byf'intermediate glass is meant glass'awhose to the rod'to the lowest "nearest to "the hard vitreous "material. Such "graded seals hiEWll known and spe'oies thereof are disclosed-in UiiS. Patent .No. 2,17%685, issued October 31,1939 to "B61 *et a1. and assigned "tvthe' assignee of this application.

Inthe-eonstruction'o! the'norniuctor-- eal body,

tubeor vitreous material "whose diameter iisfonly slightly greater than that of 'thezrod over most of the, length of thetube but is expanded'at 'the endnearthebutton to fit the outer rim'of the button, to which it is then'sealed. The narrower part of the length of the vitreous tube isithen collapsed onto the rod by heating while maintaining a vacuum within the-itube. In the case or f a tungsten rod 1 and quartz tube, therod is usually wrap'ped with a thin metal I'foi'l sheet, Ifor example, molybdenum, to prevent the quartz from sticking :to the tungsten.

At one end the tube may-be "formed into "or left "as a flange for sealingto the sides "ofa :hoie a vitreous envelope as aforementioned. At the other end of the tube-there is' inevitably left between the rod, the button and the *vitreous material a space of appreciable volume, owing i to the fact that" the collapsing of the vitreousmaterialonto the rod must 'be' limited at "this end to preserve'the shapeof the glass button.

As far as we are aware, such conductor-seal *bodies havenot been used in the manufacture of high pressure metal vapor electric discharge devices and they are not, in fact, immediately suitable for such use. For such aconductorseal body were used in the manufacture of ahigh pressure metal vaporelectric dischargedevice, such as'a lamp to introduce a conductorthrough the vitreous envelope of the 1amp,the length-pf the conductor-seal body would: have to' be such that in operation of the lamp' 'the end of'the metal rod emerging from the glass button was so far from the envelope that is was, or could be kept, suiiiciently'cool to prevent the glass button "seal beingdamaged by heat, and also toprevent any appreciable oxidation of the rod. 'Thepart 'of 'tihe body near thisend' of the rod'would therefore also be relatively-cool in operation andth'en the met'al vapor creeping f'between the vitreous tube andthe'metal rod wouldcondenseinthe -said=spaceat=the cool'end of the' tube. 'Such condensation would lead to lowering of the metal vapor pressure within the I lamp, 1 and eventually to'a reduction inlight output fromthe lamp.

"I'hepbjec't of this invention is to provide-conductor-seai bodies or the type specified in the formbfs'tems wl'iichcan be used on the envelopes'of high pressuremetal vapor electricdischarge devices. "Other objects and advantages of the invention will appear from the following description or species thereof.

Accordingto theinvention the-said space i=between the metal" rod-"the glass" button 'and'the duce such a gas or vapor; and'must not react with the metal of the rod, the tube of vitreous material or the glass button seal in a detrimental manner.

In a conductor-seal body-according to the vention, which is to be used in the manufacture of a high pressure mercury vapor lamp, powdered silica is the refractory material which we prefer to use. Silica is also suitable for use with other metal vapors such as cadmium or zinc. But other suitable powdered inert refractories such as alumina or zirconia may also be used in accordance with this invention.

The powdered material may be introduced into the expanded end of the vitreous tube just before the sealing of the tube to the outer rim of the button and before the collapsing of the tube onto the rod. The powder is preferably packed tightly into the end of the tube. The tube is then sealed to the outer rim of the button and collapsed onto the rod as before. It can be collapsed so closely onto the powder that little or no space is left at the end of the tube whichis 'not filled with powder.

The presence of the powder reduces considerably the volume of metal which can condense in the said space. But since the powder, however tightly packed, must be porous to some extent and permit the condensation of some metal, it is desirable to keep the volume of the said space as small as possible. This is preferably achieved by making the expanded end of the vitreous tube reentrant and sealing the button to the end of the tube at the bottom of the well formed by the re-entrant end. 7

In the accompanying drawing, a preferred form-of conductor-seal body in accordance with the invention, in which the volume of the said space is kept small in this way, is illustrated by way of example in Fig. l which shows the body in the form of a stem in an elevational, partly sectional view; Fig. 2 is a similar view of another species of the invention.

In the embodiment of Fig. l the glass button sealed to the metal rod conductor I consists of a sleeve 2 sealed to the rod and a dished flange 3 extending from the sleeve. The flange 3 is sealed to, so as to close, the re-entrant end 4 of the expanded end 6 of the tube 5 of hard vitreous material, along the axis of which tube the rod I passes, the tube being a close fit around the rod.

. The open end of the tube 5 is formed as a flange for sealing to the sides of a hole in the envelope of a discharge lamp. In accordance with the in- .vention, the space at the end of the tube 5 bebody of the form shown in Fig. 1 will now be described in detail, and it will be assumed, for the purposes of description that the rod is of tungsten, the hard vitreous material is quartz, the

button is of intermediate glass, and the refractory material used is silica powder.

In the initial stages of the construction a tungsten rod conductor I has sealed around it an intermediate glass button having a dished flange 3 extending from a short sleeve 2 sealed to the tungsten. To the periphery of -the flange 3 is sealed-a short length of quartz-tube 4 so as to form coaxially with the rod I the walls of a cup of which the button forms the base. This cup is dimensioned .to fit, base first, into the expanded end G'of a' quartz'tube 5 whose other end is formed as a flange suitable for sealing into a -hole in the envelope of a discharge device, and

which. is arranged to be a close but sliding fit around the foil-wrapped rod conductor I for most of the intermediate part of its length. The

thin molybdenum sheet foil wrapping around the rod Ifisshown at 8 in the drawing.

After inserting the foil-wrapped rod I into the tube 5 and the cup (2, 3, 4) into the expanded end 6 of the tube 5, held vertically with this end uppermost, finely-powdered silica 'I-is introduced into the'spacebetween the cup and the tube 5 and the tube is tapped to ensure settling and close' packing of the powder. Sufficient powder is introduced to fill all the space between the cup, the adjacent part of the rod I, and the tube (5, 6). The lengths of the tube 4 and expanded part 6 of the tube 5 are arranged so that their ends are adjacent and these ends are sealed together by heating while nitrogen is blown around the outer part of therod I and within the cup, to avoid oxidation of the tungsten. The tube 5 is then collapsed onto the foil-wrapped rod conductor along at least part of its length and is also collapsed, as far as possible, into the powder I to reduce the possibility'of there being any space left between the sealing button and the quartz tube that'is not filled with silica'powder. A vacuum is maintained within the tube 5 during the collapsing.

The clearance between the walls of the cup 2, 3, 4 and the expanded end 6 of the tube 5 should be made as small aspracticable, consistent with ensuring the safety of the intermediate glass seal during the collapsing of the quartz tube 5 onto the rod land silica powder I, in order to keep as small as possible the volume of the silicafilled space at the end of the tube.

An alternative form of conductor-seal body in accordance with the invention, which may sometimes be used, is represented in Fig. 2 of the accompanying drawing, which shows the completed conductor-seal body. Corresponding parts of Figs. 1 and 2 are referred to by the same numerals in the two figures.

' In this embodiment the sleeve 2 of the glass button is sealed around a metal rod conductor I, and the rim of the dished flange 3 of the button, extending from the'sleeve, is sealed to one end of the quartztube 4'to form a cup, the rim of which is sealed to the expanded end 6 of the tube 5 of vitreous material with the concave face of the button towards the main part of the sealbody; the rod conductor I passes through the tubesfa which is a close fit around the rod. The open end of the tube 5 is formed as a flange for sealing to the sides of a hole in the envelope of .a discharge lamp. In accordance with the invention, the space at the end of the tube 5 between the expanded end of the tube 6, the button 2, 3 and the rod I is substantially filled with inert powdered refractory material.

, A- preferred method of making a conductorseal bodyof the form shown in Fig. 2 will now be described and it will again be assumed for the purposes of description, that the rod is of tun sten, the hard vitreous material is quartz, the button is of intermediate glass, and the refractory material is silica powder.

The initial stages of the construction are as described for the previous embodiment, but the cup formed by the button 2, 3 and the short the cup, rim foremost, into proximity with the expanded end B of the tube 5. More silica powder is then introduced through the gap between the rim of the cup and the end 6, into the space formed between the quartz tubes 6 and 4 and the powder is tightly packed. by bringing the rim of the cup into abutment with the end of the expanded part orthe tube to which it is then sealed by heating while nitrogen is blown around the rod I outside the tube 5. Finally, the tube 5 is collapsed onto the foil-wrapped rod conductor and the silica powder as in the previous embodiment.

What we claim as new and desire to secure by Letters Patent of the United States is:

An elongated stem for a high pressure metal vapor electric discharge device having a quartz envelope, comprising a tungsten rod, a quartz tube closely surrounding said rod to provide mechanical support therefor, having one end adapted for fusion with the envelope of the device and being of enlarged diameter at its opposite end with a re-entrant portion at said end, and intermediate glass body hermetically uniting and constituting the sole hermetic seal between said rod and said tube and being positioned at the inner end of said re-entrant portion to close the enlarged end of said tube, and finely divided refractory inert material filling and tightly packed into the space defined by the rod, the enlarged end of the tube and the glass body to minimize condensation of metal vapor in said stem.

EVAN HERBERT NELSON. v, ERNEST BENJAMIN POWER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,159,335 Keyes Nov. 2, 1915 1,558,524 Winninghofi Oct. 27, 1925 1,639,575 Robinson Aug. 16, 1927 1,909,797 Anderson, Jr May 16, 1933 2,116,429 Gooskens May 3, 1938 2,177,714 Hagen Oct. 31, 1939 2,409,360 Kettlewell (A) Oct. 15, 1946 2,409,361 Kettlewell (B) Oct. 15, 1946 2,504,522 Greiner Apr. 18, 1950 FOREIGN PATENTS Number Country Date 476,833 England Dec. 16, 1937 520,635 England Apr. 30, 1940 

